Radiation plate and power semiconductor module IC package

ABSTRACT

Heat dissipating plate ( 4 ) made of copper-base alloy is proposed that exhibits high degree of flatness after joining in the step of assembling power semiconductor modules, IC packages, etc., that will not crack in the solder ( 3 ) joint if subjected to heat cycles during joining or in an environment of use, and that has high heat conductivity and cost effectiveness. The heat dissipating plate ( 4 ) uses a copper-base alloy having a 0.2% yield strength of at least 300 N/mm 2  which is characterized in that the 0.2% yield strength after heating at 400° C. for 10 minutes is at least 90% of the 0.2% yield strength before heating and that said copper-base alloy has a heat conductivity of at least 350 W/m·K and contains at least one element of the group consisting of Fe, Co and Ni plus P in a total amount of 0.01–0.3%; the heat dissipating plate ( 4 ) is 10–200 mm long on each side, 0.1–5 mm thick and warped by 200 μm or less in a curved shape with a radius of curvature of at least 100 mm; this heat dissipating plate ( 4 ) exhibits high degree of flatness after the assembling step and assures improved heat dissipating performance.

This application is the United States national phase application ofInternational Application PCT/JP02/08479 filed Aug. 23, 2001.

TECHNICAL FIELD

This invention relates to a heat dissipating plate that uses copper-basealloys and which is to be employed in semiconductor apparatuses such aspower semiconductor modules and IC packages.

BACKGROUND ART

Power semiconductor modules are semiconductor apparatuses that arecomposed of a semiconductor device (1), a copper pattern (14), aninsulating substrate (15), a conductor layer (16) and a heat dissipatingplate (4) and they are extensively used in home electronic appliancessuch as air conditioners and washing machines, as well as in automobilesand industrial machines.

The recent trend of IC packages as in PCs is toward higher density andgreater sophistication in functions; as a result, heat generation hasbecome an important problem to deal with and the heat dissipating plate(4) called “a heat spreader” is currently used. Since the heat generatedfrom power semiconductor modules and IC packages must be efficientlydissipated, the heat dissipating plate (4) is required to have high heatconductivity.

Other diverse characteristics are required of the heat dissipating plate(4). Take, for example, a power semiconductor module; in the assemblingstep, a metal-ceramics joined board (2) (hereunder referred to as“joined board (2)”) and the heat dissipating plate (4) are joined bysolder (3) and the integrity of the solder (3) joint is important; alsoimportant is the flatness of the heat dissipating plate (4) since it ismounted on a heat sink.

During use, the power semiconductor module is subject to extensivetemperature changes depending upon the operating situation and stress isexerted on the solder (3) joint between the joined board (2) and theheat dissipating plate (4) that have different thermal expansioncoefficients. During such heat cycles, no defects such as crackingshould occur in the solder (3) joint.

Speaking of the heat dissipating plate (4) that is to be used in ICpackages, the reliability of the joint to the semiconductor chip isimportant; the heat dissipating plate (4) that is to be used in BGApackages and the like needs sufficient strength (rigidity) to serve as aback plate. Its strength (rigidity) should not drop in the assemblingstep.

Thus, the heat dissipating plate (4) to be used in power semiconductormodules and IC packages must satisfy diverse requirements including goodheat conductivity; further, their prices are desirably low in view ofthe declining prices of home electronic appliances and PCs.

As the material (9) to be used in the heat dissipating plate (4),Cu—Cu₂O, Al—SiC, Cu—W and other combined systems that are close to theinsulating substrate (15) and IC chips in terms of thermal expansioncoefficient may be considered but they are not cost-effective, nor dothey have adequate heat conductivity.

Instead, copper-base alloys that have high heat conductivity and arealso advantageous costwise are extensively used. Oxygen-free copper,which has high heat conductivity and is common as the material (9) forthe heat dissipating plate (4), does not provide adequate 0.2% yieldstrength for the material (9) and hence is not capable of preventing thedeformation of the heat dissipating plate (4) which is also required towork as a reinforcement. In addition, the heat dissipating plate (4)needs to be heated at 200–350° C. for several minutes in the joiningstep. If oxygen-free copper is heated under this condition, the material(9) will soften, making it difficult to achieve the desired flatness ofthe heat dissipating plate (4) after assembly.

Aside from oxygen-free copper, Cu—Zr, Cu—Ag, Cu—Sn, Cu—Sn—P andCu—(Fe,Co,Ni)—P systems are practical copper-base alloys having highheat conductivity. However, the P-free Cu—Zr, Cu—Ag and Cu—Sn systemswill have higher oxygen concentration if they are melted and solidifiedin the atmosphere during casting. To deal with this problem, a facilitycapable of atmosphere control is required but this causes a disadvantagein terms of production cost. The Cu—Zr and Cu—Ag systems are alsodisadvantageous in terms of the prices of their ingredients. Further,the Cu—Ag system is not satisfactory in 0.2% yield strength andheat-resisting characteristic; as for the Cu—Sn system, there occursinsufficiency in 0.2% yield strength and heat-resisting characteristicif the Sn concentration is low whereas there occurs a drop in heatconductivity if the Sn concentration is high. The Cu—Sn—P system hassimilar characteristics to the Cu—Sn system. Although conventionally notrecognized as the material (9) for the heat dissipating plate (4), theCu—(Fe,Co,Ni)—P system is a precipitation-strengthening type copper-basealloy and has good balance between physical properties. (0.2% yieldstrength and heat resistance) and electrical conductivity.

However, the above-mentioned copper-base alloys have thermal expansioncoefficients of 16×10⁻⁶˜18 ×10⁻⁶/K whereas of all AlN, Al₂O₃, etc. whichare used in the insulating substrate (15) of the power semiconductormodule, and Si, etc. which are used in semiconductor chips have thermalexpansion coefficients of less than 10×10⁻⁶/K; hence, in the case ofusing those copper-base alloys as the material (9) for the heatdissipating plate (4), the reliability of the joint during assembly hasbeen a problem to address.

Consider, for example, the power semiconductor module; if the heatdissipating plate (4) is joined to the joined board (2) by means ofsolder (3), the former will warp due to the thermal expansion mismatchas the solder (3) solidifies (see FIG. 3). If such warped heatdissipating plate (4) is screwed to a heat sink, the area of contact isso small that the required heat dissipating quality cannot be obtained.If the heat sink and the heat dissipating plate (4) are joined by meansof an increased number of screws with a view to increasing the area oftheir contact, cracking may occur in the solder (3) joint or theinsulating substrate (15) may break. Therefore, the flatness of the heatdissipating plate (4) after assembly has been a problem to address.

The present invention has been accomplished in view of these problemsand has as an object providing the heat dissipating plate (4) that issuitable for use in semiconductor apparatuses such as powersemiconductor modules and IC packages and which is inexpensive, has highheat conductivity and assures a highly reliable joint during assemblyand use.

DISCLOSURE OF THE INVENTION

This invention provides the heat dissipating plate. (4) which uses acopper-base alloy that has high heat conductivity, that does not causethe material (9) to soften as the result of heating during assembly andthat has high rigidity as a reinforcement; the invention also providesthe heat dissipating plate (4) that is controlled in size and amount ofwarpage in accordance with joining conditions such as joiningtemperature, time and the area of a joint with a view to achieving areliable joint and a highly flat heat dissipating plate (4) byovercoming the thermal expansion mismatch with the insulating substrate(15) of a power semiconductor module and the semiconductor chip in an ICpackage; the invention further provides a power semiconductor module andan IC package using the above-mentioned heat dissipating plates (4).

Thus, the present invention provides the following:

-   1. a heat dissipating plate (4) which is a copper-base alloy having    a 0.2% yield strength of at least 300 N/mm² and a heat conductivity    of at least 350 W/m·K;-   2. a heat dissipating plate (4) which is a copper-base alloy having    a 0.2% yield strength of at least 300 N/mm² and a heat conductivity    of at least 350 W/m·K and further characterized in that the 0.2%    yield strength after heating at 400° C. for 10 minutes is at least    90% of the 0.2% yield strength before said heating;-   3. a heat dissipating plate (4) which is a copper-base alloy having    a 0.2% yield strength of at least 300 N/mm² and a heat conductivity    of at least 350 W/m·K and further characterized in that the crystal    grain size after heating at 400° C. for 10 minutes is no more than    25 μm;-   4. a heat dissipating plate (4) which is a copper-base alloy having    a 0.2% yield strength of at least 300 N/mm² and a heat conductivity    of at least 350 W/m·K and further characterized in that the 0.2%    yield strength after heating at 400° C. for 10 minutes is at least    90% of the 0.2% yield strength before said heating and that the    crystal grain size after said heating is no more than 25 μm;-   5. the heat dissipating plate (4) according to any one of 1–4 above,    wherein said copper-base alloy contains at least one element    selected from the group consisting of Fe, Co and Ni plus P in a    total amount of 0.01–0.3 wt % (the wt % used to describe the alloy's    composition is hereunder referred to simply as %), with the balance    being incidental impurities and copper;-   6. the heat dissipating plate (4) according to any one of 1–5 above,    which is a square or a rectangle each side of which is 10–200 mm    long and warped by 200 μm or less, said heat dissipating plate (4)    being 0.1–5 mm thick;-   7. the heat dissipating plate (4) according to any one of 1–5 above,    which is a square or a rectangle each side of which is 10–200 mm    long and warped in a curved shape with a radius of curvature of at    least 100 mm, said heat dissipating plate (4) being 0.1–5 mm thick;-   8. the heat dissipating plate (4) according to any one of 1–5 above,    which is a square or a rectangle each side of which is 10–200 mm    long and warped by 200 μm or less in a curved shape with a radius of    curvature of at least 100 mm, said heat dissipating plate (4) being    0.1–5 mm thick;-   9. a power semiconductor module or an IC package which use the heat    dissipating plate (4) according to any one of 1–8 above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a power semiconductor module;

FIG. 2 shows in a plan and a side view the heat dissipating plate (4)with its length and amount of warpage indicated;

FIG. 3 is a side view illustrating the restoring force of the heatdissipating plate (4);

FIG. 4A is a side view showing the heat dissipating plate (4) as warpedin a curved shape;

FIG. 4B is a side view showing the heat dissipating plate (4) as warpedin a V shape;

FIG. 4C is a side view showing the heat dissipating plate (4) as warpedin a W shape;

FIG. 5 is a side view of an apparatus for heating the heat dissipatingplate (4);

FIG. 6 is a sectional view of an apparatus for pressing a strip ofcopper-base alloy;

FIG. 7 shows in a plan and a side view of the joined board (2); and

FIG. 8 is a side view of an apparatus for measuring the amount ofwarpage of the heat dissipating plate (4).

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described below in a specific way. The heatdissipating plate (4) needs to work as a reinforcement (as a backplate), so it must have mechanical strength. As-assembled powersemiconductor modules and IC packages are required not to deform; inother words, the heat dissipating plate (4) itself is required not todeform. In this respect, a measure for the ability of the copper-basealloy used in the heat dissipating plate (4) to withstand deformation is0.2% yield strength. This characteristic is particularly required of athin-walled heat dissipating plate (4) and it can be prevented fromdeforming if it has a 0.2% yield strength of at least 300 N/mm². Below300 N/mm², an IC package will deform during assembly and use and itsoperational reliability will drop. Preferably, a 0.2% yield strength ofat least 350 N/mm² is desired.

For processing the heat dissipating plate (4), etching may be performedto shape it if it is a heat spreader; however, pressing is moreadvantageous in terms of cost. If pressing is to be performed, it isdifficult to feed the material (9) into a mold unless it does not havesufficient strength to keep it flat. If the 0.2% yield strength is atleast 300 N/mm², pressing can be performed smoothly; below 300 N/mm², itbecomes difficult to feed the material (9) into the mold and punch itout with high precision.

The major role of the heat dissipating plate (4) is to absorb the heatgenerated from the semiconductor device (1) and transfer and release itto the outside. Power semiconductor modules are experiencing greatersophistication in their functions whereas the CPU of PCs is experiencingnot only this but also effort toward higher density; in either case,more heat is generated and the heat dissipating plate (4) having highheat conductivity is required. It is therefore necessary that thematerial (9) to be used in the heat dissipating plate (4) have heatconductivity of at least 350 W/m·K. Below 350 W/m·K, the heat generatedfrom the semiconductor device (1) during use cannot be adequatelytransferred to the heat sink and the operational reliability of powersemiconductor modules and IC packages will drop.

The heat dissipating plate (4) is joined to the joined board (2) in thecase of a power semiconductor module and to the semiconductor device (1)in the case of an IC package. When it is joined, the heat dissipatingplate (4) is heated at 200–350° C. for several minutes. If this heatingcauses the material (9) to soften, the heat dissipating plate (4) of anIC package cannot work as a back plate. In the case of a powersemiconductor module, the heat dissipating plate (4) cannot remain flatbut warps. Even if the warped heat dissipating plate (4) is joined to aheat sink, the area of contact is so small that the heat dissipatingquality of the plate will decrease. Furthermore, on account of the heatcycles during assembly and use, cracking may potentially occur in thesolder (3) joint.

It is therefore necessary that the material (9) not soften upon heatingat 400° C. for 10 minutes which is considered the joining condition thatapplies the greatest amount of heat in practice; in other words, the0.2% yield strength of the heat dissipating plate (4) after this heatingmust be at least 90% of the initial 0.2% yield strength. Preferably, nodrop in the 0.2% yield strength is desired.

In the case of joining the heat dissipating plate (4) of a powersemiconductor module to the joined board (2), if solder (3) solidifies,there occurs warpage due to the thermal expansion mismatch between theinsulating substrate (15) and the heat dissipating plate (4). With asubsequent lapse of time, the solder (3) creeps, causing the heatdissipating plate (4) to deform (restore). The amount of warpage thatoccurs during solidification of the solder (3) is attributable to the0.2% yield strength and heat resistance of the material (9) used in theheat dissipating plate (4), as well as to the size of the joined board(2) and the heating condition. Therefore, in order to ensure flatness,the heat dissipating plate (4) must be warped as shown in FIG. 2considering the change (restoration) that will occur over time afterjoining. To describe the warp of the heat dissipating plate (4), theplane that is to be joined to the joined board. (2) is considered theupper surface; then, the warp is taken positive if it is convexdownward, and negative if it is convex upward. If the amount of the warpis negative, it is totally useless in restoration after joining and noflatness is obtained after joining. If the warp is greater than +200 μm,spaces or voids are likely to occur in the joint between the joinedboard (2) and the heat dissipating plate (4) and the integrity of thejoint will deteriorate. In addition, it becomes difficult to warp theheat dissipating plate (4) and disadvantages occur in terms ofproductivity and cost. Hence, the amount of the warp must not exceed 200μm. Preferably, it is not more than 100 μm.

The shape of the warp to be created in the heat dissipating plate (4) isdesirably curved as shown in FIG. 4A. Even if a V-shaped warp (see FIG.4B) or a W-shape warp (see FIG. 4C) is created in the same amount,spaces or voids are likely to occur in the joint between the joinedboard (2) and the heat dissipating plate (4) and between thesemiconductor device (1) and the heat dissipating plate (4),deteriorating the integrity of the joints. In addition, the insulatingsubstrate may potentially break in the power semiconductor module. Thisproblem might occur in the curved warp of FIG. 4A depending on itsshape.

Irrespective of whether the warp is as shown in FIG. 4A or 4B or 4C, theproblems described above can be solved by adjusting it to have a certainradius of curvature and upwards. If the warp's radius of curvature is atleast 100 mm, the integrity of the joint will not deteriorate, nor willthe insulating substrate break. If a plurality of curves are formed asshown in FIG. 4C, all of them will suffice to have a radius of curvatureof at least 100 mm.

The heat dissipating plate (4) to be warped in the manner describedabove is also subject to size and thickness limitations. The shape ofthe heat dissipating plate (4) is generally a square or a rectangle. Upto 10 holes of no more than Φ 20 mm may be bored through the heatdissipating plate (4) in order to screw it down to a heat sink.Depending on the use, corners of the square or rectangle may be suitablyworked. Speaking of the size and thickness of the heat dissipating plate(4), if the length of one side is less than 10 mm or greater than 200 mmand if the thickness is less than 0.1 mm or greater than 5 mm, it isdifficult to warp the heat dissipating plate; in particular, if thelength of one side exceeds 200 mm and the plate thickness exceeds 5 mm,a larger facility is required and a disadvantage will occur in terms ofcost.

Speaking of the material (9) to be used in the heat dissipating plate(4), if the crystal grain size after heating in the assembling step isgreater than 25 μm, it is likely to experience increased variations andthe mechanical characteristic values of the plate will differ from onearea to another; as a result, there will be no restoring force of thetype shown in FIG. 3. Hence, the material (9) to be used in the heatdissipating plate (4) must have a crystal grain size not exceeding 25 μmafter heating at 400° C. for 10 minutes. Preferably, a crystal grainsize of no more than 20 μm is desired.

In order to meet the requirements that the heat conductivity be at least350 W/m·K, the 0.2% yield strength be at least 300 N/mm², no softeningoccur upon heating at 400° C. for 10 minutes and that the productioncost be low, copper-base alloys that utilize (Fe,Co,Ni)—P precipitatesare suitable. Two common means for improving the 0.2% yield strength andheat resistance of copper-base alloys are precipitation strengtheningand solid-solution strengthening. Precipitation-strengthening typecopper-base alloys, as compared with solid-solution strengthening typecopper-base alloys, can be improved in terms of 0.2% yield strength andheat resistance without lowering heat conductivity. Among suchprecipitation-strengthening type copper-base alloys, those which utilize(Fe,Co,Ni)—P precipitates are particularly used since they areadvantageous from the manufacturing viewpoint in terms of materials andequipment costs.

In utilizing the (Fe,Co,Ni)—P precipitates, at least one of Fe, Co andNi plus P must be contained in a total amount of 0.01–0.3%. Below0.0.01%, the amount of the precipitate is too small to provide adequate0.2% yield strength and heat resistance. Beyond 0.3%, the required heatconductivity is not obtained.

The following are examples of the invention but they are by no meansintended to limit the invention.

EXAMPLE 1

Copper-base alloy Nos. 1˜5 for use in the heat dissipating plate (4) ofthe invention and comparative copper-base alloy Nos. 6˜16, with theirchemical ingredients (unit of measurement: %) being shown in Table 1,were melted in a rf induction melting furnace to cast ingots of40×40×150 (mm). From those ingots, test pieces (8) of 40×40×30 (mm) werecut, homogenized at 900° C. for 60 minutes, hot rolled to 8.0 mm,water-cooled and pickled. Thereafter, cold rolling, annealing and coldrolling were repeated to prepare test pieces (8) in plate form with athickness of 3.0 mm.

TABLE 1 Alloy Fe + Co + No. system Fe Co Ni P Ni + P Others Cu Invention1 Cu—Fe—P 0.05 0.02 0.07 bal. samples 2 Cu—Fe—P 0.08 0.03 0.11 bal. 3Cu—Co—P 0.11 0.035 0.145 bal. 4 Cu—Fe—Co—P 0.06 0.04 0.036 0.136 bal. 5Cu—Fe—Ni—P 0.15 0.06 0.05 0.26 bal. Comparative 6 Cu(C1020) >99.9samples 7 Cu(C1020) >99.9 8 Cu—Zr Zr: 0.10 bal 9 Cu—Ag Ag: 0.10 bal 10 Cu—P 0.03 0.03 bal 11  Cu—Sn Sn: 0.15 Bal 12  Cu—Sn—P 0.006 0.006 Sn:0.15 bal 13  Cu—Ni—Sn—P 0.15 0.05 0.20 Sn: 0.07 bal 14  Cu—Mg—P 0.120.12 Mg: 0.20 bal 15  Cu—Fe—P 0.006 0.002 0.008 bal 16  Cu—Fe—Ni—P 0.200.15 0.07 0.42 bal

The thus prepared copper-base alloy Nos. 1–16 were evaluated for heatconductivity, 0.2% yield strength, 0.2% yield strength and crystal grainsize after heating at 400° C. for 10 minutes, and Vickers hardness (seeTable 2). Heat conductivity was calculated from electrical conductivity,and electrical conductivity, 0.2% yield strength and. Vickers hardnesswere measured in accordance with JIS H 0505, JIS Z 2241 and JIS Z 2244,respectively. For heating at 400° C. for 10 minutes, an apparatus of thedesign shown in FIG. 5 was used. Crystal grain size measurementconsisted of grinding the surface of the material (9) with an emeryboard, buffing, etching and examination under an optical microscope.

The production cost was evaluated considering the raw material costincurred in production with the actual equipment and the rate of rejectsthat failed to meet the quality requirement; ◯ refers to a sample of lowproduction cost; Δ refers to a sample that had any one of threeproblems, high cost of additive element, low product quality and theneed to perform a special treatment during production; x refers to asample that had at least two of these problems.

TABLE 2 0.2% yield strength (N/mm²) Crystal grain after size (μm)Vickers Heat heating at after heating hardness conductivity before 400°C. for at 400° C. for Production No. (HV) (W/m · K) heating 10 min 10min cost Invention 1 109 364 313 309 20 ◯ samples 2 114 358 350 345 17 ◯3 115 360 381 377 18 ◯ 4 130 358 400 385 11 ◯ 5 121 353 389 372 14 ◯Comparative 6 110 395 348  62 70 ◯ samples 7 104 394 283 260 51 ◯ 8 119369 382 376 15 X 9 114 380 331 286 31 Δ 10  109 336 350 268 40 ◯ 11  114342 341 291 29 ◯ 12  108 332 337 289 38 ◯ 13  120 286 372 369 20 ◯ 14 152 328 520 494 10 X 15  104 376 308 142 53 ◯ 16  136 310 450 442 14 ◯

The copper-base alloys that had been subjected to the measurementsdescribed above were pressed with an apparatus of the design shown inFIG. 6. The pressed alloys were in plate form which was a rectanglehaving the longer side X (=100 mm) and the shorter side Y (=50 mm) asshown in FIG. 2, with the longer side warped in a curved shape ofd_(x)=+80 μm as shown in FIG. 4A. The warp had a radius of curvature of1200 mm. To each of the pressed plates, a joined board (2) (see FIG. 7)was joined by means of solder (3). The solder (3) was H60A of JIS Z3282. The joining condition was 350° C. for 7 minutes. Right after thejoining, the amount of warpage was measured; it was also measured when10 hours, 50 hours and 100 hours had passed after the joining. Theresults are shown in Table 3. The amount of warpage was measured with anapparatus of the design shown in FIG. 8 which used a dial gage (17). Thetest results were evaluated in terms of the degree of flatness thatremained after 100 hours. A sample was considered to have passed thetest when the residual warpage was within 0±50 μm.

TABLE 3 0.2% yield Amount of warpage dx (μm) strength (N/mm²) rightafter before after heating joining joining at 400° C. to to Degreebefore for joined joined after after after of No. heating 10 min boardboard 10 hr 50 hr 100 hr flatness Invention 1 313 309 80 −196 −84 −63−41 ◯ samples 2 350 345 80 −184 −80 −60 −38 ◯ 3 381 377 80 −173 −61 −39−21 ◯ 4 400 385 80 −168 −56 −34 −18 ◯ 5 389 372 80 −175 −64 −41 −24 ◯Comparative 6 348  62 80 −250 −220 −220 −220 X samples 7 283 260 80 −240−150 −145 −140 X 8 382 376 80 −177 −65 −46 −28 ◯ 9 331 286 80 −228 −110−94 −82 X 10  350 268 80 −240 −147 −141 −135 X 11  341 291 80 −208 −90−78 −57 X 12  337 289 80 −218 −103 −87 −68 X 13  372 369 80 −180 −73 −53−31 ◯ 14  520 494 80 −130 −20 −6 +8 ◯ 15  308 142 80 −242 −210 −204 −197X 16  450 442 80 −156 −41 −16 −3 ◯

As can be seen from the results shown in Tables 2 and 3, inventionsample Nos. 1˜5 could be produced at low cost, had high heatconductivity, adequate mechanical strength and assured high degree offlatness after joining to the joined board (2). Therefore, the samplesof the invention will provide a good heat dissipating plate (4) suitablefor use in power semiconductor modules, IC packages etc.

On the other hand, sample No. 7 which had a 0.2% yield strength of lessthan 300 N/mm² and a crystal grain size in excess of 25 μm after heatingat 400° C. for 10 minutes, as well as sample Nos. 6, 9˜12 and 15 ofwhich the 0.2% yield strength after heating at 400° C. for 10 minuteswas less than 90% of the initial value and which had a crystal grainsize in excess of 25 μm after heating at 400° C. for 10 minutes causedthe material (9) to soften during joining with solder (3) and theflatness of the material (9) was not restored by the passage of timeafter the joining; hence, the amount of warpage that remained when 100hours had passed after the joining to the joined board (2) was so greatthat the flatness of the heat dissipating plate (4) was low. Sample Nos.13, 14 and 16, which satisfied the criterion for evaluating the amountof warpage, had heat conductivity of less than 350 W/m·K and were poorin heat dissipating performance. Sample No. 8 satisfied the criterionfor evaluating the amount of warpage and exhibited efficient heatdissipation; however, since it used Zr, the raw material cost was high;in addition, the Zr—O oxides caused adverse effects on quality duringhot rolling, so sample No. 8 was also unacceptable in terms ofproduction cost.

EXAMPLE 2

Using copper-base alloy No. 1 of the invention having the compositionshown in Table 1 (see Example 1) and copper-base alloy Nos. 17˜22 of thesame composition as No. 1, we investigated the size of warp that wascreated by pressing and the flatness of the pressed plate that remainedafter joining to the joined board (2). Copper-base alloy Nos. 1 and17˜22 were pressed with the apparatus shown in FIG. 6. The pressedalloys were in plate form which was a rectangle having the longer side X(=100 mm) and the shorter side Y (=50 mm) as shown in FIG. 2. The longerside of each sample was warped in a curved shape as shown in FIG. 4A;for the amounts of warp, see Table 4.

The thus pressed plates were joined to the joined board (2). The methodof joining, the method of measuring the degree of flatness and thecriteria for evaluating the amount of warp after joining to the joinedboard (2) were the same as in Example 1. The integrity of the joint wasevaluated by checking to see if cracking occurred within 100 hours afterjoining to the joined board (2): x, cracked; ◯, not cracked. The ease ofwarping was evaluated by the following criteria: x, the apparatus ofFIG. 6 alone could not create warp and correction with a leveler (10)and a hammer was necessary; ◯, warping was possible by the apparatus ofFIG. 6.

TABLE 4 Amount of warpage dx (μm) right before after joining joining toto Degree Integrity Ease joined joined after after after of of the ofNo. board board 10 hr 50 hr 100 hr flatness joint warping Invention  1+80 −196 −84 −63 −41 ◯ ◯ ◯ samples 17 +30 −230 −96 −74 −48 ◯ ◯ ◯ 18 +130−150 −58 −49 −26 ◯ ◯ ◯ 19 +200 −61 +8 +24 +31 ◯ ◯ ◯ Comparative 20 −20−260 −117 −94 −75 X ◯ ◯ samples 21 +250 −17 +31 +42 +48 ◯ X X 22 +300+29 +68 +77 +81 X X X

As one can see from the results shown in Table 4, invention alloy Nos. 1and 17˜19 had high degree of flatness after they were joined to thejoined board (2); in addition, no defects such as cracking occurred inthe solder (3) joint and the samples could be easily warped. On theother hand, sample No. 20 that was warped in an amount of less than 0 μmhad low degree of flatness after it was joined to the joined board (2);sample Nos. 21 and 22 that were warped in an amount of more than 200 μmhad low integrity of the solder (3) joint since cracking occurred in it;in addition, sample Nos. 21 and 22 could not be easily warped.Therefore, the samples of the invention will provide a good heatdissipating plate (4) suitable for use in power semiconductor modules.

EXAMPLE 3

Using copper-base alloy Nos. 23˜32 of the same composition ascopper-base alloy No. 1 of the invention having the composition shown inTable 1 (see Example 1), we investigated the shape of plates and theease with which they could be warped. Test pieces (8) in plate form witha thickness of 8.0 mm were prepared from the copper-base alloys of thesame composition as copper-base alloy No. 1 in accordance with theproduction method of Example 1; thereafter, cold rolling and annealingwere repeated to prepare test pieces (8) in plate form having variousthicknesses as shown in Table 5 for Nos. 23˜32. The thus producedcopper-base alloy Nos. 23˜32 were pressed with the apparatus shown inFIG. 6. The pressed alloys in plate form were of the sizes shown inTable 5 and warped in the amounts also shown in Table 5; the warpedplates were of a curved shape as shown in FIG. 4A. The value “0 μm” asthe amount of warpage was tested in order to investigate the flatness ofan as-punched plate without warping it after pressing.

Sample Nos. 23˜27 shown in Table 5 had shapes in the scope of theinvention whereas sample Nos. 28˜32 had comparative shapes; 10 pieces ofeach sample were pressed. The ease of warping was evaluated by thenumber of plates that has to be corrected with the leveler (10) and ahammer. The amount of warpage was evaluated by checking to see if therequirement of the target value ±10 μm was met.

TABLE 5 Plate Length (mm) Amount of thickness longer shorter warpage inthe Ease of No. (mm) side side longer side (μm) warping Invention 230.30 100 50 0 ± 10 0/10 samples 24 0.30 100 50 100 ± 10  0/10 25 0.30150 100  0 ± 10 0/10 26 1.00 100 50 0 ± 10 0/10 27 3.00 100 50 0 ± 100/10 Comparative 28 0.08 100 50 0 ± 10 2/10 samples 29 0.30 250 180  100± 10  1/10 30 1.00 250 180  100 ± 10  3/10 31 3.00 250 180  100 ± 10 5/10 32 6.00 100 50 0 ± 10 3/10

As one can see from the results shown in Table 5, none of sample Nos.23˜27 having shapes in the scope of the invention required platecorrection after pressing and they all had good press formability. Thus,the samples of the invention, which could be produced efficiently onpress while exhibiting high degree of flatness after being punched onpress, will provide a good heat dissipating plate (4) suitable for usein power semiconductor modules and IC packages. On the other hand,sample No. 28 with a plate thickness of less than 0.1 mm, sample No. 32with a plate thickness in excess of 5 mm and sample. Nos. 29˜31 thelonger sides of which were longer than 200 mm had a common problem ofvariations in the amount of warpage and, hence, they could not be warpedsatisfactorily.

EXAMPLE 4

Using copper base alloy Nos. 33˜39 of the same composition ascopper-base alloy No. 1 of the invention having the composition shown inTable 1 (see Example 1), we investigated the shape of warp and theintegrity of the solder (3) joint between the joined board (2) and theheat dissipating plate (4). The copper-base alloys having the samecomposition as the invention sample No. 1 were pressed with theapparatus shown in FIG. 6. The pressed alloys were in plate form whichwas a rectangle having the longer side X (=100 mm) and the shorter sideY (=50 mm) as shown in FIG. 2, with the longer side warped in an amountof d_(x)=+80 μm and curved with the radii shown in Table 6. Either onecurve or three curves were provided as shown in FIG. 4A or 4C. Whenthree curves were provided, the center one had the smallest radius ofcurvature. The thus pressed plates were joined to the joined board (2).The method of joining, the method of measuring the degree of flatnessand the criteria for evaluating the amount of warpage were the same asin Example 1. The integrity of the joint was evaluated by checking tosee if cracking occurred within 100 hours after joining to the joinedboard (2): x, cracked; ◯, not cracked.

TABLE 6 Amount of Amount of warpage warpage (μm) (μm) before after 100Radius of joining to hours of Integrity No. of curvature the joinedjoining to the of the No. curves (mm) board joined board joint Invention33 1 1500 +80 −38 ◯ samples 34 1 800 +80 −42 ◯ 35 1 100 +80 −45 ◯ 36 3500 +80 −44 ◯ Comparative 37 1 50 +80 −63 X samples 38 3 80 +80 −59 X 393 30 +80 −72 X

As one can see from the results shown in Table 6, invention sample Nos.33˜36 all had high degree of flatness after joining to the joined board(2) and no cracking occurred in the solder (3) joint. On the other hand,sample Nos. 37˜39 having radii of curvature less than 100 mm had lowdegree of flatness and cracking occurred in the solder (3) joint. SampleNos. 38 and 39 even cracked in the insulating substrate (15). Therefore,the samples of the invention will provide a good heat dissipating plate(4) suitable for use in power semiconductor modules.

INDUSTRIAL APPLICABILITY

As will be clear from the foregoing examples, the heat dissipating plate(4) using the copper-base alloys of the invention is satisfactory instrength, heat-conductivity, heat resistance and press formability,assures a highly reliable joint during assembly and use and can beproduced at low cost. Therefore, using this heat dissipating plate (4),one can provide power semiconductor modules, IC packages and othersemiconductor apparatuses having good characteristics.

1. A heat dissipating plate which comprises a copper-base alloy having a0.2% yield strength of at least 300 N/mm² and a heat conductivity of atleast 350 W/m·K, said alloy containing P and at least one elementselected from the group consisting of Fe, Co and Ni, said P and said atleast one element being in a total amount of 0.01 to 0.3 wt %, said heatdissipating plate being a square or rectangle, each side of which is 10to 200 mm long and warped by 200 μm or less, and said heat dissipatingplate being 0.1 to 5 mm thick.
 2. The heat dissipating plate accordingto claim 1, which is warped in a curved shape with a radius of curvatureof at least 100 mm.
 3. A power semiconductor module or an IC packagewhich use the heat dissipating plate according to claim
 2. 4. A powersemiconductor module or an IC package which use the heat dissipatingplate according to claim
 1. 5. A heat dissipating plate which comprisesa copper-base alloy having a 0.2% yield strength of at least 300 N/mm²and a heat conductivity of at least 350 W/m·K, wherein the 0.2% yieldstrength after heating at 400° C. for 10 minutes is at least 90% of the0.2% yield strength before said heating, said alloy containing P and atleast one element selected from the group consisting of Fe, Co and Ni,said P and said at least one element being in a total amount of 0.01 to0.3 wt %, said heat dissipating plate being a square or rectangle, eachside of which is 10 to 200 mm long and warped by 200 μm or less, andsaid heat dissipating plate being 0.1. to 5 mm thick.
 6. The heatdissipating plate according to claim 5, which is warped in a curvedshape with a radius of curvature of at least 100 mm.
 7. A powersemiconductor module or an IC package which use the heat dissipatingplate according to claim
 6. 8. A power semiconductor module or an ICpackage which use the heat dissipating plate according to claim
 5. 9. Aheat dissipating plate which comprises a copper-base alloy having a 0.2%yield strength of at least 300 N/mm², a heat conductivity of at least350 W/m·K, and a crystal grain size after heating at 400° C. for 10minutes being no more than 25 μm, said heat dissipating plate being asquare or a rectangle, each side of which is 10 to 200 mm long, saidalloy containing P and at least one element selected from the groupconsisting of Fe, Co and Ni, said P and said at least one element beingin a total amount of 0.01 to 0.3 wt %, said heat dissipating plate beinga square or a rectangle, each side of which is 10 to 200 mm long andwarred by 200 μm or less, and said heat dissipating plate being 0.1 to 5mm thick.
 10. The heat dissipating plate according to claim 9, which iswarped in a curved shape with a radius of curvature of at least 100 mm.11. A power semiconductor module or an IC package which use the heatdissipating plate according to claim
 10. 12. A power semiconductormodule or an IC package which use the heat dissipating plate accordingto claim
 9. 13. A heat dissipating plate which is a copper-base alloyhaving a 0.2% yield strength of at least 300 N/mm² and a heatconductivity of at least 350 W/m·K, wherein the 0.2% yield strengthafter heating at 400° C. for 10 minutes is at least 90% of the 0.2%yield strength before said heating and the crystal grain size after saidheating is no more than 25 μm, said heat dissipating plate being asquare or a rectangle, each side of which is 10 to 200 mm long, saidalloy containing P and at least one element selected from the groupconsisting of Fe, Co and Ni, said P and said at least one element beingin a total amount of 0.01 to 0.3 wt %, said heat dissipating plate beinga square or a rectangle, each side of which is 10 to 200 mm long andwarped by 200 μm or less, and said heat dissipating plate being 0.1 to 5mm thick.
 14. The heat dissipating plate according to claim 13, which iswarped in a curved shape with a radius of curvature of at least 100 mm.15. A power semiconductor module or an IC package which use the heatdissipating plate according to claim
 14. 16. A power semiconductormodule or an IC package which use the heat dissipating plate accordingto claim 13.